Hydrodynamic Impacts of Expanding Aquaculture

Climate change may potentially change aquatic systems and bring certain risks for aquaculture development. Understanding interactions between aquaculture and the environment helps to ensure aquaculture expansion is sustainable in the future. It is critical to determine how farms influence tidal flow patterns, turbulence, mixing and material transport in estuaries. This research aims to determine the flow response of an oyster farm, predict how expanding farms and farm placement will alter estuarine dynamics, and understand how the design of a farm influences material transport. The hydrodynamic response of a floating oyster aquaculture farm in a low inflow estuary (the Damariscotta River estuary) is investigated using hourly field observations covering both neap and spring tidal conditions and an idealized numerical model. Given the importance of lateral processes in estuaries, particularly those with channel complexities such as channel bends, we hypothesize that the farm-imposed drag force will affect the nearby dynamics in the channel and that the farm effects will not be localized to the farm area. A bulk drag coefficient for the whole farm, as well as for a single oyster cage was derived and implemented into an idealized regional scale model to qualitatively repeat patterns observed from field. The qualitative consistency between field observation and idealized model results provides valuable insight into the hydrodynamic response of a floating oyster farm. The field observations also depicted a reversal in subtidal flow patterns compared with those typically expected in an elongated estuary. To better understand the mechanisms driving subtidal flow reversal, a semi-analytical model for a low inflow estuary with farm drag force was developed. The model captured surface flow reduction and flow bypassing, consistent with field observations. Without the farm, subtidal flows were laterally sheared with inflow on the right-hand side and outflow on the left. The reduction of tidal flow from drag force in farm area resulted in tidally averaged along channel advection at the seaward and landward farm boundaries that drove subtidal flows into the farm. Inside the farm, the reduced tidal currents near the surface combined with upwelling and downwelling at the channel-shoal interface to produce tidally rectified flow, which altered the subtidal flow structure compared to the case with no farm. The transport of Lagrangian particles demonstrated how various farm expansion scenarios hindered seaward long-term transport in the estuary portions upstream of the farm. The semi-analytical hydrodynamic model combined with a material transport model was further applied to investigate the sensitivity of farm layout to food uptake, which showed that a bluff layout (wide and narrow) was optimal since more nutrients can be transported into the farm through wider landward or seaward boundary. Expanding individual farm size decays filtration per unit area in the farm, where the filtration over a tidal cycle per unit area yields a logarithmic decay with length expansion and hyperbolic decay with width expansion. Therefore, the feedback between the hydrodynamics and the farm can deteriorate the food supply. Additionally, in shallow estuarine locations, bottom generated turbulence can overcome weak stratification to transport bottom sediment upward, resulting high near surface turbidity that might negatively impact oyster growth. Based on the linkage between near surface turbidity to tidal mixing, and stratification a critical depth for farm siting was proposed to minimize surface water turbidity. Outcomes from this work highlight the importance of understanding interactions between aquaculture and environments. The hydrodynamic and hydrographic conditions that control species growth factors are highly variable and site specific, therefore acquiring detailed environmental data and thoughtfully evaluating interactions between aquaculture and the environment are beneficial approaches for farm planning. Both a field data collection strategies and modeling tools from this work can be used to promote environmental and economical sustainability in aquaculture expansion in the future

ChatGPT for Software Security: Exploring the Strengths and Limitations of ChatGPT in the Security Applications

ChatGPT, as a versatile large language model, has demonstrated remarkable potential in addressing inquiries across various domains. Its ability to analyze, comprehend, and synthesize information from both online sources and user inputs has garnered significant attention. Previous research has explored ChatGPT's competence in code generation and code reviews. In this paper, we delve into ChatGPT's capabilities in security-oriented program analysis, focusing on perspectives from both attackers and security analysts. We present a case study involving several security-oriented program analysis tasks while deliberately introducing challenges to assess ChatGPT's responses. Through an examination of the quality of answers provided by ChatGPT, we gain a clearer understanding of its strengths and limitations in the realm of security-oriented program analysis.Comment: 1 Table, 8 figure

距離独立集合問題および誘導マッチング問題に対する近似アルゴリズム

This thesis deals with the following two problems, the Maximum Distance-d Independent Set problem (MaxDdIS for short) and the Maximum Induced Matching problem (MaxIM for short), where d ≥ 3. We design some approximation algorithms to solve MaxDdIS and MaxIM. (1) We first study MaxDdIS. Our main results for MaxDdIS are as follows: (i) It is NP-hard to approximate MaxD3IS on 3-regular graphs within 1.00105 unless P=NP. (ii) For every fixed integers d ≥ 3 and r ≥ 3, MaxDdIS on r-regular graphs is APX-hard, and show the inapproximability of MaxDdIS on r-regular graphs. (iii) We design polynomial-time O(rd-1)-approximation and O(rd-2/d)- approximation algorithms for MaxDdIS on r-regular graphs. (iv) We sharpen the above O(rd-2/d)-approximation algorithms when restricted to d = r = 3, and give a polynomial-time 2-approximation algorithm for MaxD3IS on cubic graphs. (v) Furthermore, we design a polynomial-time 1.875-approximation algorithm for MaxD3IS on cubic graphs. (vi) Finally, we consider planar graphs and obtain that MaxDdIS admits a polynomial-time approximation scheme (PTAS) for planar graphs. (2) We then investigate MaxIM on r-regular graphs. For subclasses of r-regular graphs, several better approximation algorithms are known. The previously known best approximation ratios for MaxIM on C5-free r-regular graphs and C3, C5 -free r-regular graphs are (3r/4 - 1/8 + 3/16r - 8) and (0.7084r + 0.425), respectively. We design a (2r/3 + 1/3) -approximation algorithm, whose approximation ratio is strictly smaller/better than the previous one for C5-free r-regular graphs when r ≥ 6, and for {C3, C5 }-free r-regular graphs when r ≥ 3.九州工業大学博士学位論文 学位記番号：情工博甲第339号 学位授与年月日：平成31年3月25日1 Introduction|2 Preliminaries|3 Maximum Distance-d Independent Set problem|4 Maximum Induced Matching Problem|5 Conclusion九州工業大学平成30年

Microstructure evolution under tribological loading and its elementary mechanisms

Tribologie, die Lehre und Technologie von aufeinander wirkenden Oberflächen in Relativbewegung, ist von großer Bedeutung für viele Aspekte des alltäglichen Lebens. Reibung und Verschleiß von metallischen Werkstoffen sind zentral für die Energieeffizienz und Dauerhaftigkeit vieler Produkte, vom Verbrennungsmotor bis hin zu künstlichen Gliedmaßen oder Gelenken. Veränderungen der Mikrostruktur unterhalb der Oberfläche von Materialien unter tribologischer Belastung sind nicht immer kontinuierlich, selbst unter milden Gleitbedingungen. Sehr häufig wurden verschiedene tribologisch induzierte Schichten parallel zur Gleitrichtung beobachtet. Diese können oft durch unterschiedliche Korngrößen innerhalb der Schichten sowie einer scharfen Grenze dazwischen unterschieden werden. Diese Grenze ist eine Diskontinuität in der Mikrostruktur und von besonderem Interesse, da sie die Oberflächenschicht vom darunterliegenden Grundmaterial trennt. Die Oberflächenschicht ist der Bereich, in dem der reale Kontakt stattfindet, die chemischen Reaktionen an der Oberfläche ablaufen und Verschleißpartikel erzeugt werden. Die Bildungsmechanismen dieser Diskontinuität sind noch unklar. Ziel dieser Arbeit ist es, den Ursprung dieser Diskontinuität mittels eines soweit wie möglich vereinfachten tribologischen Experiments zu untersuchen: dem einmaligen Übergleiten einer hochreinen Kupferprobe mit einer Saphirkugel. Dieses Experiment erzeugt ein typisches Merkmal - eine als „Versetzungsstreifen“ (dislocation trace line) bezeichnete, scharfe Linie, die etwa 100 nm unter der Oberfläche mittels (Raster-) Transmissionselektronenmikroskopie beobachtet werden kann. Diese wird als eine selbst-organisierte Versetzungsstruktur interpretiert, welche durch einen Vorzeichenwechsel im Schubspannungsfeld in der Probe verursacht wird, hervorgerufen durch den gleitenden Gegenkörper auf der Oberfläche. Der Versetzungsstreifen ist der Ursprung der mikrostrukturellen Diskontinuität und sein Einfluss auf die Mikrostruktur bleibt auch für weitere tribologische Belastungen maßgeblich. Durch die Betrachtung der Mikrostrukturentwicklung in verschiedenen Stadien tribologischer Beanspruchung konnten die Bildung von Versetzungsnetzwerken, das Wachstum einer tribologisch induzierten Schicht sowie Oberflächenoxidation beobachtet werden. Auf Basis der Beobachtungen wurden die Elementarmechanismen aufgedeckt sowie eine zeitliche Abfolge dieser grundlegenden Prozesse vorgeschlagen. In diesem Zusammenhang wird die tribologisch induzierte Oberflächenoxidation detailliert, als charakteristischer Vorgang an der Probenoberfläche, untersucht. Das tribologische Verhalten des Systems – hauptsächlich durch die Oberflächenschicht bestimmt – wird maßgeblich durch die chemischen Reaktionen an der Oberfläche während der mittleren und späten Stadien der tribologischen Beanspruchung beeinflusst. Der Pfad, auf dem Sauerstoff aufgrund der tribologisch induzierten Oxidation in das Kupfer eintritt, wird aufgedeckt. Ein Mechanismus für die Bildung von amorphem/nanokristallinem Kupfer(I)-oxid wird vorgeschlagen. Dieses Wissen ist von wesentlicher Bedeutung, da durch das Verständnis der Mechanismen ein Maßschneidern von Oberflächen hinsichtlich verbessertem tribologischem Verhalten möglich wird. Diese Arbeit umfasst die komplette Mikrostrukturentwicklung in hochreinem Kupfer in Kontakt mit Saphirkugeln. Sie trägt zum grundlegenden Wissen bei, welches ein tieferes Verständnis von Verformungsmechanismen unter tribologischer Beanspruchung erlaubt. Des Weiteren beinhaltet diese Arbeit unverzichtbare Informationen für Modelle, welche darauf abzielen, das Verhalten eines Tribosystems hinsichtlich der Entwicklung von Reibung und Verschleiß vorherzusagen - insbesondere in frühen Stadien des Gleitens

STUDY ON ARRANGEMENT OF COOLING WATER PIPE TO CONTROL HYDRATION HEAT OF CONCRETE IN BEAM OF CABLE-STAYED BRIDGE

The box girder joint section of the Yangtze River Highway Bridge is taken as the research background, and the finite element software MIDAS/FEA is used to simulate the hydration heat of concrete to the layout of cooling water pipe in building mass concrete. The finite element calculation results are in well agreement with the measured data. On this basis, the influence of changing the diameter and distance of the cooling water pipe, the inlet temperature and the flow rate on the temperature of hydration heat is studied. The results show diameter of the cooling water pipe and inlet temperature have a significant effect on the temperature of hydration heat. The change of water flow rate has little effect on the temperature of hydration heat. It provides a reference for the layout of the same concrete cooling water pipe arrangement

Which Features are Learned by CodeBert: An Empirical Study of the BERT-based Source Code Representation Learning

The Bidirectional Encoder Representations from Transformers (BERT) were proposed in the natural language process (NLP) and shows promising results. Recently researchers applied the BERT to source-code representation learning and reported some good news on several downstream tasks. However, in this paper, we illustrated that current methods cannot effectively understand the logic of source codes. The representation of source code heavily relies on the programmer-defined variable and function names. We design and implement a set of experiments to demonstrate our conjecture and provide some insights for future works.Comment: 1 table, 2 figure

Tribological performance and microstructural evolution of α-brass alloys as a function of zinc concentration

Tailoring a material’s properties for low friction and little wear in a strategic fashion is a long-standing goal of materials tribology. Plastic deformation plays a major role when metals are employed in a sliding contact; therefore, the effects of stacking fault energy and mode of dislocation glide need to be elucidated. Here, we investigated how a decrease in the stacking fault energy affects friction, wear, and the ensuing sub-surface microstructure evolution. Brass samples with increasing zinc concentrations of 5, 15, and 36 wt% were tested in non-lubricated sphere-on-plate contacts with a reciprocating linear tribometer against Si$_{3}$N$_{4}$ spheres. Increasing the sliding distance from 0.5 (single trace) to 5,000 reciprocating cycles covered different stages in the lifetime of a sliding contact. Comparing the results among the three alloys revealed a profound effect of the zinc concentration on the tribological behavior. CuZn15 and CuZn36 showed similar friction and wear results, whereas CuZn5 had a roughly 60% higher friction coefficient (COF) than the other two alloys. CuZn15 and CuZn36 had a much smaller wear rate than CuZn5. Wavy dislocation motion in CuZn5 and CuZn15 allowed for dislocation self-organization into a horizontal line about 150 nm beneath the contact after a single trace of the sphere. This feature was absent in CuZn36 where owing to planar dislocation slip band-like features under a 45° angle to the surface were identified. These results hold the promise to help guide the future development of alloys tailored for specific tribological applications